And they are most likely still doing it, everybody does.
I would be really amazed if Binance wouldn't do it, after all, CZ is the guy behind the faking at OKCoin, he was the one supervising it.
Bithumb was caught with more than 90%, Huobi the same, and it's quite mind-boggling to see an exchange that brags of a volume x10 more that of Coibabse falling behind in terms of revenue another ten times.
The whole thing can be faked, the number of users can be done by importing a database with random names and ids and emails, Facebook and tweets likes, comments, share can be bought with useless tokens, viewers can be bought online in packs of millions, even app downloads can be faked.
But it all comes to the surface when everyone does, and you end up with really really stupid claims, as 20% 30% of the population owning crypto, with 10% of them having made transactions with BTC, where the hell do you cram all that usage in a blockchain with just 600m of them and another 300 on ETH?
I would split by at least 5 every claim of users and volume any exchange makes!
Ten years fast forward and we are going to keep wondering about the same thing.